Percentage of voting equity interests acquired at the acquisition date in the business combination.

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The cash outflow to reacquire common stock during the period.

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Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

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The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

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Number of shares of stock issued during the period pursuant to acquisitions.

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Number of new stock issued during the period.

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Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.

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The number of shares authorized to be repurchased by an entity's Board of Directors under a stock repurchase plan.

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The remaining number of shares authorized to be repurchased by an entity's Board of Directors under a stock repurchase plan.

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Number of shares that have been repurchased during the period and are being held in treasury.

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Stockholders' Equity (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended			1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 31, 2014	Jul. 31, 2014	Apr. 30, 2013	Oct. 26, 2009
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	10,000,000us-gaap_PreferredStockSharesAuthorized	10,000,000us-gaap_PreferredStockSharesAuthorized
Preferred Stock, Par or Stated Value Per Share	$ 0.001	$ 0.001
Common stock, shares authorized to repurchase (in shares)							8,000,000
Remaining number of shares available to be repurchased	3,335,448
Common stock repurchases (in shares)	626,234us-gaap_TreasuryStockSharesAcquired	688,128us-gaap_TreasuryStockSharesAcquired
Payments for repurchase of common stock	$ 29	$ 19	$ 13
Stock Issued During Period, Value, New Issues		15
U.S. Medical Management [Member]
Class of Stock [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired				68.00%
Stock Issued During Period, Shares, Acquisitions				4,486,434
Community Health Solutions [Member]
Class of Stock [Line Items]
Stock Issued During Period, Shares, Acquisitions					1,492,738
Acaria Health [Member]
Class of Stock [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired						100.00%
Stock Issued During Period, Shares, Acquisitions						3,433,380
Stock Issued During Period, Shares, New Issues						685,280
Stock Issued During Period, Value, New Issues						$ 15